Method and apparatus for UE mobility in a small cell system

ABSTRACT

The present application discloses a method for a master eNB (MeNB) handover or a secondary eNB (SeNB) handover in a small cell system, comprising: sending by a source MeNB information of a source secondary cell (Scell) to a target MeNB; sending by the target MeNB a message to the source MeNB, the message notifying the source MeNB to suspend data transmission on a bearer of the SeNB. Until a message of data transmission resuming is received, the data transmission/reception is started to continue. The method for a MeNB handover or a SeNB handover provided in the present application may reduce the reconfiguration of the bearer for the UE, avoid releasing the bearer by error, and improve the system throughput and the data rate of transmission.

PRIORITY

This application is a continuation application of prior application Ser.No. 15/114,987, filed on Jul. 28, 2016, which issued as U.S. Pat. No.9,888,412 on Feb. 6, 2018, and was a National Phase Entry of PCTInternational Application No. PCT/KR2015/000789, which was filed on Jan.26, 2015, and claims a priority to Chinese Patent Application No.201410041300.4, which was filed on Jan. 28, 2014, and claims a priorityto Chinese Patent Application No. 201410851469.6, which was filed onDec. 31, 2014, the contents of each of which are incorporated herein byreference.

TECHNICAL FIELD

The present application relates to wireless communication technologies,and more particularly, to a method and an apparatus for a secondary eNB(SeNB) handover and/or a master eNB (MeNB) handover in a small cellsystem.

BACKGROUND ART

Current mobile communication is more and more tending to providemultimedia service with high rate transmission to users.

FIG. 1 shows a system architecture of System Architecture Evolution(SAE).

As shown in FIG. 1, a user equipment (UE) 101 is a terminal device forreceiving data. Evolved Universal Terrestrial Radio Access Network(E-UTRAN) 102 is a wireless access network, comprising a macro basestation (eNodeB/NodeB) which may provide the UE an interface foraccessing the wireless network. A mobility management entity (MME) 103is responsible for managing mobility context, session context andsecurity information of the UE. A serving gateway (SGW) 104 mainlyprovides the user-plane functions. The MME 103 and the SGW 104 may belocated in the same physical entity. A packet data network gateway (PGW)105 is responsible for functions, such as charging, monitoring, and mayalso be located in the same physical entity with the SGW 104. A policyand charging rules function entity (PCRF) 106 provides policy andcharging rules of quality of service (QoS). A serving General PacketRadio Service (GPRS) support node (SGSN) 108 is a network node deviceproviding routing for data transmission in Universal MobileTelecommunications System (UNITS). A home subscriber server (HSS) 109 isa home subsystem of the UE, responsible for protecting information ofthe UE, including current location of the UE, an address of a servingnode, security information of the UE, packet data context of the UE,etc.

The 3rd Generation Partnership Project (3GPP) has proposed requirementsof small cell enhancement in release 12 (Rel-12). Target scenarios ofthe small cell enhancement include scenarios with macro cell coverageand without macro cell coverage, indoor and outdoor, ideal and non-idealbackhaul enhancement, as shown in FIG. 2.

In the case with macro cell coverage, it has been proposed to apply atechnique of carrier aggregation at different base stations. A macrocell and a small cell may work in different bands. There are two kindsof architectures that apply the technique of carrier aggregation atdifferent base stations, i.e., one based on Radio Access Network (RAN)split, and the other based on Core Network (CN) split, for theuser-plane data. The architecture based on CN split means that for abearer established on a pico cell, the user-plane data is directly sentby the CN SGW to the pico cell, but not forwarded by the macro cell.

In the architectures of small cells, the UE may simultaneously transmitand receive data to and from two base stations, named asdual-connectivity, in which only one base station is responsible forsending a Radio Resource Control (RRC) message to the UE, andinterconnect with the CN control-plane entity MME, such base stationnamed as MeNB, and the other named as SeNB. One cell in the MeNB for theUE is a primary cell (Pcell) of the UE, through which a RRC message issent to the UE, and other cells are secondary cells (Scells). One cellamong the Scells of the SeNB is a primary Scell of the SeNB (pScell),providing functions of the pScell. There is a physical uplink controlchannel in the pScell, but none in other Scells. A cell group of theMeNB is named as MCG, and a cell group of the SeNB is named as SCG.Configurations of SCG at the UE side are performed by the SeNB, which issent from the MeNB to the UE via a RRC container. The MeNB does notparse the RRC container, or parse but not modify the configurations inthe RRC container.

When a UE moves, or the channel quality changes, the MeNB can determineto handover the Scell to a new base station, which becomes the new SeNB,called as a SeNB handover, or the MeNB can determine to handover thePcell to a new base station, which becomes the target MeNB, called as aMeNB handover. During the MeNB handover process, an existing method isto switch all the bearers to the target MeNB, of which the disadvantagesare frequent reconfiguration of the bearers, and lack of efficientutilization of the dual connectivity to improve the system throughputand transmission rate of the UE. During the SeNB handover process,according to an existing method, the secondary bearers are establishedat a new SeNB, and the new SeNB configures the bearer at the UE side.After the bearer establishment is successful, the MeNB sends the bearerrelease to the source SeNB. It is possible for the source SeNB toconfigure the bearers at the UE side according to existing methods, soit may occur that the newly established bearers at the UE side would bereleased. Therefore, the present application relates to the method forthe MeNB handover, in which the target MeNB selects the source SeNB asthe target SeNB, and further relates to the method for the SeNBhandover, in which the MeNB handovers a SeNB to another base station.

In accordance with another aspect of the present disclosure, anapparatus for supporting a user equipment (UE) mobility in a small cellsystem is provided. The apparatus is configured to perform the method ofone of claims 1 to 14.

Therefore, a need exists for a method and an apparatus for UE mobilityin a small cell system.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present disclosure.

DISCLOSURE Technical Problem

Aspects of the present disclosure are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentdisclosure is to provide a method and an apparatus for a MeNB handoverand/or a SeNB handover, which may reduce the reconfiguration of thebearer for the UE.

Another aspect of the present disclosure is to provide a method and anapparatus for avoiding releasing the bearer by error, and improving thesystem throughput and the data rate of transmission.

Technical Solution

In accordance with an aspect of the present disclosure, a method for aSeNB handover in a small cell system is provided. The method comprises:sending, by a MeNB, a message to a target MeNB or a target SeNB, themessage carrying information of a bearer to be established; sending, bythe target MeNB or by the target SeNB, a response message to the MeNB;sending, by the MeNB, a bearer release request message to a source SeNB,the bearer release request message carrying an indication information toindicate whether the source SeNB needs to release a bearer or a Scell ata UE side; and sending, by the source SeNB, a bearer release responsemessage to the MeNB.

After the message is received by the source SeNB, when the message doesnot carry indication information, or indication information is carriedto indicate the bearer at the UE side needs to be configured, the sourceSeNB releases the configurations related to the secondary bearer or theScell at this eNB, and releases the secondary bearer or the Scell at theUE side, for example, by configuring a release bearer list, which atleast includes an identifier of the Scell or the secondary bearer. Suchconfiguration is included in a RRC container to send from the sourceSeNB to the MeNB and to the UE. When an indication information iscarried, and the indication information indicates the bearer at the UEside doesn't need to be configured, the source SeNB releases theconfigurations related to the secondary bearer or the Scell at this eNB,but does not need to release the secondary bearer or the S cell at theUE side, and not need to send the RRC container to the MeNB.

The indication information may also be an indication of SeNB handover,an indication of release locally, or an indication of releasing allresources.

The bearer release response message sent by the source SeNB to the MeNBis optional.

Preferably, it also comprises that the MeNB sends a RRC reconfigurationrequest message to the UE. A list of the Scells or the secondary bearersto be released within in the said RRC reconfiguration request message isconfigured by the MeNB.

In accordance with another aspect of the present disclosure, a methodfor a MeNB handover and/or a SeNB handover in a small cell system isprovided. the method comprises: sending, by a source MeNB, informationof a source SeNB to a target MeNB, the information of the source SeNBincluding an identifier of a bearer, a base station identifier of asource Scell or a cell identifier of the source Scell; sending, by thetarget MeNB, a message to the source MeNB.

The target MeNB determines whether a certain bearer may be establishedat the source SeNB, according to the information of the source SeNB sentfrom the source MeNB, QoS information of the bearer and measurementreport of a UE.

When the target SeNB and the source SeNB are the same, the message sentfrom the target MeNB to the source MeNB carries an identifier of abearer and an identifier of the target SeNB or Scell, or the messagecarries an indicator of source bearer suspending.

Preferably, it also comprises that the source MeNB sends a bearerrelease request message to the source SeNB, the message including thebearer information for the bearer release, e.g., an identifier of thebearer or the Scell, and/or the information for the bearer unrelease(i.e., bearer suspending), e.g., an identifier of the bearer or theScell, an indicator of the bearer suspending. Alternatively, the sourceMeNB sends a bearer suspending message to the source SeNB, the messagecarrying an identifier of the S cell or the secondary bearer.

According to the received information of the bearer suspending, thesource SeNB is aware that a certain bearer is still being established atthis SeNB, and pauses the data transmission/reception at this bearer,waiting for receiving a message of data transmission resuming sent bythe target MeNB. When received, the SeNB starts continuing the datatransmission/reception.

Preferably, it also comprises that the target MeNB sends a bearerresuming message to the source SeNB. After the target MeNB receives apath switch response, the target MeNB notifies the source SeNB to startcontinuing the data transmission/reception.

In accordance with another aspect of the present disclosure, a methodfor a user equipment (UE) handover in a small cell system is provided.The method comprises: sending, by a source master eNB (MeNB), a handoverrequest message to a target MeNB, the handover request message carryinginformation of a source secondary eNB (SeNB); sending, by the targetMeNB, a SeNB addition request message to a target SeNB, to establish adata bearer in the target SeNB; sending, by the target SeNB, a SeNBaddition response message to the target MeNB; sending, by the targetMeNB, a handover response message to the source MeNB; and sending, bythe source MeNB, a SeNB release request message to the source SeNB.

It can be seen from the above technical scheme that the method for aMeNB handover and/or a SeNB handover provided in the present applicationmay reduce the reconfiguration of the bearer for the UE, avoid releasingthe bearer by error, and improve the system throughput and the data rateof transmission.

Other aspects, advantages, and salient features of the disclosure willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses various embodiments of the present disclosure

DESCRIPTION OF DRAWINGS

The above and other aspects, features, and advantages of certainembodiments of the present disclosure will be more apparent from thefollowing description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram illustrating an existing SAE systemarchitecture;

FIG. 2 is a schematic diagram illustrating deployment scenarios of smallcell enhancement;

FIG. 3 is a schematic diagram illustrating a method according to a firstembodiment of the present application;

FIG. 4 is a schematic diagram illustrating a method according to asecond embodiment of the present application;

FIG. 5 is a schematic diagram illustrating a method according to a thirdembodiment of the present application; and

FIG. 6 is a schematic diagram illustrating a method according to afourth embodiment of the present application.

FIG. 7 is a block diagram illustrating an eNB according to an embodimentof the present application.

Throughout the drawings, like reference numerals will be understood torefer to like parts, components, and structures.

MODE FOR INVENTION

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of variousembodiments of the present disclosure as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the various embodiments describedherein can be made without departing from the scope and spirit of thepresent disclosure. In addition, descriptions of well-known functionsand constructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of the presentdisclosure. Accordingly, it should be apparent to those skilled in theart that the following description of various embodiments of the presentdisclosure is provided for illustration purpose only and not for thepurpose of limiting the present disclosure as defined by the appendedclaims and their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the term “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to skill in theart, may occur in amounts that do not preclude the effect thecharacteristic was intended to provide.

The present application is further described in detail hereinafter withreference to the accompanying drawings to make the objective, technicalsolution and merits thereof more apparent.

FIG. 3 is a schematic diagram illustrating a method for a SeNB handoverin a small cell system according to an embodiment of the presentapplication, in which a MeNB determines to handover one SeNB to anotherwithout any change of the MeNB. It includes the following blocks.

In block 301, the MeNB sends a bearer addition request message to atarget SeNB.

The MeNB determines to establish a bearer at a new SeNB. The bearer maybe established previously at the source SeNB or at the MeNB, or may be anew bearer configured by the MME. The bearer addition request messagemay include an identifier of the bearer, QoS information of the bearer,UE capability information, etc.

The target SeNB determines the configuration information of the bearerfor the UE according to the QoS information of the bearer and UEcapability. The configuration information of the secondary bearer or theScell for the UE is included in the RRC container by the target SeNB,and then the RRC container is sent to the UE via the MeNB. Thus, UE mayconfigure its protocol stacks according to the configuration, e.g.,Radio Link Control (RLC), Media Access Control (MAC).

In block 302, the target SeNB sends a bearer addition response messageto the MeNB, the message carrying configuration information of thesecondary bearer or the Scell for the UE.

As described above, the configuration information of the secondarybearer or the Scell for the UE, which is configured by the target SeNB,is included in the RRC container and then the RRC container is sent tothe MeNB.

The MeNB may not parse the RRC container, and forward it to the UE.Alternatively, the MeNB may parse the RRC container to determine whetherthe configuration by the target SeNB can satisfy the requirements of UEcapability. If not, the MeNB may reject the configurations from thetarget SeNB.

In block 303, the MeNB sends a RRC reconfiguration request message tothe UE.

In block 304, the MeNB sends a bearer release request message to thesource SeNB.

There are two cases in this regard. A first case is that the bearerpreviously established at the SeNB is established at a new SeNB in block301. For this case, the bearer of the source SeNB is re-established atthe target SeNB, which means that this bearer still belongs to the SCG,and the identifier of the secondary bearer or Scell is not changed. Thecorresponding new configuration information has been already configuredby the target SeNB in the above steps, and sent to the UE by the MeNB.Hence, the source SeNB doesn't need to reconfigure the secondary beareror the Scell where the bearer is established for the UE, and not need togenerate a RRC container. However, if it is unknown for the source SeNB,it might still configure the secondary bearer or the Scell for the UE.When the secondary bearer or Scell release message is received by thesource SeNB in block 304, the source SeNB will configure a secondarybearer or Scell release list, which includes the identifier of the Scellor the secondary bearer. Then the SeNB sends the list included in theRRC container to the UE via the MeNB. After the new configurationinformation is received, the UE could release the secondary bearer orScell, which is newly established in block 303, therefore, an erroroccurs.

A second case is that the bearer established at the target SeNB in block301 is different from the bearer previously established at the sourceSeNB. The bearer previously established at the source SeNB may becurrently established at the MeNB as a Pcell or primary bearer, or itmay still belong to the SCG but the identifier of the bearer or theScell has been changed. For this case, the source SeNB needs tore-configure the Scell where the bearer is established for the UE and togenerate a RRC container, which is then included in the bearer releaseresponse.

To identify those two cases, the MeNB includes indication information inthe bearer release request message sent to the SeNB, to indicate whetherthe SeNB needs to configure the secondary bearer or Scell for the UE,needs to generate a RRC container and further sends it to the MeNB.According to the indication, there are two kinds of operations at theSeNB. For example, one operation is according to the indication of “NOconfiguration”. When such indication is included in the bearer releaserequest message, the SeNB is aware that it doesn't need to re-configurethe secondary bearer or the Scell for the UE (i.e., not produce arelease list for the UE), and not need to generate a RRC container tofurther send to the MeNB, but just needs to release the information ofbearers stored on the SeNB. In addition, when it is the last bearer, italso needs to release the information of the UE, and send a releaseacknowledgement message to the MeNB. When such indication is notincluded in the bearer release request message, the SeNB needs tore-configure the secondary bearer or the Scell for the UE, with the newconfiguration information included in a RRC container, for example, theidentifier of the S cell or the secondary bearer to be released isincluded in a release list, and the release list is included in the RRCcontainer to further send to the MeNB. If no such indication informationis included, the source SeNB needs to configure the bearer or Scell forthe UE, generate new configuration in the RRC container, e.g. includingthe released Scell or bearer identifier into the release list, andincluding the released list into the RRC container and send it to theMeNB. Another operation is according to an indication of“Configuration”. If so, the SeNB needs to re-configure bearers at theUE; if not, not re-configure the bearers at the UE. In a word, theindication information is able to indicate two different operations forthe SeNB, so that according to the indication, it is optional for theSeNB to perform one of the above two operations.

In another embodiment, about the Scell release, the Scell release listfor the UE is configured by the MeNB. The MeNB sends the RRCreconfiguration request message to the UE, in which the informationabout Scell release is configured by the MeNB. In specific, there are aScell adding list, a reconfiguration list and a Scell release list inthe RRC reconfiguration request message. In the Scell release list,there is the identifier of bearer or Scell to be released, which is setby the MeNB. In the Scell adding list or the reconfiguration list, theconfiguration of the Scell or the secondary bearer is set by the SeNB.

There are also an Internet Protocol (IP) address and a tunnel endpointidentifier (TEID) for data forwarding included in the bearer releaserequest message.

In block 305, the source SeNB sends a bearer release response message tothe MeNB.

In block 306, the source SeNB sends a sequence numbering (SN) statusmessage to the MeNB, the message carrying the Packet Data ConvergenceProtocol (PDCP) SN of the secondary bearer. When the bearer isestablished at the new SeNB, the message may be sent from the MeNB tothe new SeNB.

In block 307, according to the information for the data forwarding inblock 304, the SeNB forwards the data based on the corresponding IPaddress and TEID. When the bearer is established at the new SeNB, thedata may be sent from the source SeNB to the new SeNB.

In block 308, the UE sends a RRC reconfiguration complete message to theMeNB.

In block 309, UE starts the random access procedure to synchronize withthe new SeNB. After the random access procedure is completed, the newSeNB may notify the MeNB the information of random access success ifneeded.

In block 310, the MeNB sends a path switch request message to the MME,the message including the bearer and the corresponding IP address andTEID for downlink reception. Then the message is sent from the MME tothe SGW, which is omitted herein.

In block 311, the MME sends a path switch response message to the MeNB,the message including the uplink IP address and TEID allocated by theSGW.

Using the method as described in FIG. 3, it enables the source SeNB notto generate the unnecessary configuration information for the UE, and toavoid the source SeNB releasing the secondary bearer which is newlyestablished.

FIG. 4 is a schematic diagram illustrating a method for a MeNB handoverin a small cell system according to an embodiment of the presentapplication, in which a MeNB determines to handover the MeNB to anothereNB and all the bearers at the SeNB are switched to a target MeNB. Itincludes the following blocks.

In block 401, a source MeNB sends a handover request message to a targetMeNB.

The MeNB determines to establish a bearer at the target MeNB. The bearermay be established previously at the source SeNB or at the source MeNB.The handover request message may include an identifier of the bearer,QoS information of the bearer, UE capability information, etc.

In block 402, the target MeNB sends a handover response message to thesource MeNB, the message carrying configuration information of thebearer for the UE, which is configured by the target MeNB. The messageis carried via a RRC container. In addition, the message includes theidentifier of the bearer that is established successfully.

The MeNB may not parse the RRC container, and forward it to the UE.

In block 403, the MeNB sends a RRC reconfiguration request message tothe UE.

In block 404, the MeNB sends a bearer release request message to thesource SeNB.

The SeNB is not aware whether the MeNB is changed. For the case ofnon-MeNB handover, the SeNB shall configure the Scell or the secondarybearer for the UE, and this configuration is included within a RRCcontainer to send to the UE via the MeNB. For the case of MeNB handover,all of the bearers are established at the target MeNB, which may sendthe configuration of the bearers to the UE through a RRC container. Itis not necessary for the source SeNB to configure the S cell or thesecondary bearer for the UE; otherwise, it is possible to release thebearer newly established by the target MeNB by error. Hence, there isindication information included in the bearer release message sent fromthe MeNB to the SeNB, e.g., a handover indicator is included to indicatewhether the SeNB shall configure the secondary bearer or the Scell forthe UE, and generate a RRC container to send to the MeNB. When suchindication is included, the SeNB is known that it doesn't need toreconfigure the secondary bearer or the S cell for the UE, and not needto include a RRC container, but simply to release the information of thebearer stored at the eNB. When it is the last bearer, it also needs torelease the information of the UE, and send a release acknowledgementmessage to the MeNB. When such indication is not included, the SeNBneeds to re-configure the secondary bearer or the Scell for the UE, withthe new configuration information included in a RRC container, forexample, the identifier of the S cell or the secondary bearer to bereleased is included in a release list, and the release list is includedin the RRC container to further send to the MeNB. Similar to the firstembodiment, there are also some other ways with respect to theindication information. In a word, the indication is able to indicatetwo different operations for the SeNB, so that according to theindication, it is optional for the SeNB to perform one of the above twooperations.

In another embodiment, about the bearer release, the bearer release listfor the UE is configured by the MeNB. The MeNB sends the RRCreconfiguration request message to the UE, in which the informationabout bearer release is configured by the MeNB. In specific, there are aScell adding list, a reconfiguration list and a Scell release list inthe RRC reconfiguration request message. In the Scell release list,there is the identifier of bearer or Scell to be released, which is setby the MeNB. In the Scell adding list or the reconfiguration list, theconfiguration of the Scell or the secondary bearer is set by the SeNB.

Using the above-described method, it enables the source SeNB not togenerate the unnecessary configuration information for the UE, and toavoid the source SeNB releasing the secondary bearer which is newlyestablished.

There are also the identifier of the secondary bearer or Sell, anInternet Protocol (IP) address and a tunnel endpoint identifier (TEID)for data forwarding included in the bearer release request message.

In block 405, the source SeNB sends a bearer release response message tothe MeNB.

In block 406, the source SeNB sends a sequence numbering (SN) statusmessage to the MeNB. The message may carry the PDCP SN of the secondarybearer, and may be sent from the MeNB to the target MeNB.

In block 407, the source MeNB and the source SeNB forward the data onthe bearer based on the corresponding IP address and TEID.

In block 408, the UE sends a RRC reconfiguration complete message to theMeNB.

In block 409, the MeNB sends a path switch request message to the MME,the message including the bearer and the corresponding IP address andTEID for downlink reception. Then the message is sent from the MME tothe SGW, which is omitted herein.

In block 410, the MME sends a path switch response message to the MeNB,the message including the uplink IP address and TEID allocated by theSGW.

Using the method as described in FIG. 4, it enables the source SeNB notto generate the unnecessary configuration information for the UE, and toavoid the source SeNB releasing the secondary bearer which is newlyestablished.

FIG. 5 is a schematic diagram illustrating a method for a MeNB handoverin a small cell system according to an embodiment of the presentapplication, in which a MeNB determines to handover the MeNB to anotherand the target MeNB determines the bearer is maintained as beingestablished at the source SeNB. It includes the following blocks.

In block 501, a source MeNB sends a handover request message to a targetMeNB. The message carries the information of SeNB, which may include theeNB identifier or cell identifier of the Scell.

The handover request message also includes an identifier of the bearer,QoS information of the bearer, UE capability information, etc.

In block 502, the target MeNB sends a handover response message to thesource MeNB, the message carrying configuration information of thebearer for the UE, which is configured by the target MeNB. The messageis carried via a RRC container. In addition, the message includes theidentifier of the bearer that is established successfully.

According to a measurement report and the information of the sourceSeNB, the target MeNB determines to continue using the source SeNB asthe target SeNB. The secondary bearer originally established at thesource SeNB is not switched to the target MeNB, i.e., still held at thesource SeNB. Hence, it is unnecessary to perform the frequent process ofbearer establishment and release. The handover response message in block502 includes the identifier of the bearer that is establishedsuccessfully, and the identifier of the target SeNB or Scell, or anindicator of the source bearer suspending.

In block 503, the source MeNB sends a bearer release request message tothe source SeNB. The message includes the bearer information for thebearer release, e.g., an identifier of the bearer or Scell, and/or theinformation for the bearer unrelease (i.e., bearer suspending), e.g., abearer identifier or a Scell identifier, an indication of the bearersuspending. Alternatively, the source MeNB sends a bearer suspendingmessage to the source SeNB, the message carrying an identifier of thesecondary bearer or the Scell.

In block 504, the MeNB sends a RRC reconfiguration request message tothe UE.

According to the received message in block 502, when in the message, thetarget SeNB or the eNB where the target Scell is located is the same asthe source SeNB, the source MeNB is able to determine that a certainbearer is still being established at the source SeNB. Alternatively whenthe message in block 502 indicates that a certain bearer will suspend,which is previously established at the source SeNB, the source MeNBsends a bearer suspending message to a source SeNB, the message mayinclude the identifier of the bearer, the indicator of bearersuspending, or the message may also include the identifier of the bearerto be released, or may include an indicator in combination with themethod in the first embodiment or the second embodiment. The same blocksas the first embodiment or the second embodiment and the correspondingdescription are omitted herein. After the bearer suspending message isreceived, the source SeNB is aware that a certain bearer is still beingestablished at this SeNB, and suspends the data transmission/receptionon this bearer, waiting for receiving a message of data transmissionresuming sent by the target MeNB. When received, the SeNB resumes thedata transmission/reception.

In block 505, the source SeNB sends a SN status message to the targetMeNB. The message may carry the PDCP SN of the secondary bearer.

In block 506, the source MeNB forwards the data on the bearer based onthe corresponding IP address and TEID.

In block 507, the UE sends a RRC reconfiguration complete message to theMeNB.

In block 508, the MeNB sends a path switch request message to the MME,the message including the bearer and the corresponding IP address andTEID for downlink reception. Then the message is sent from the MME tothe SGW, which is omitted herein.

In block 509, the MME sends a path switch response message to the targetMeNB, the message including the uplink IP address and TEID allocated bythe SGW.

In block 510, the target MeNB sends a bearer resuming message to theSeNB. After the path switch response message is received, the targetMeNB notifies the source SeNB to start continuing datatransmission/reception.

Using the method as described in FIG. 5, it enables the source SeNB tocontinually work during the MeNB handover process, and to avoid thefrequent bearer release and addition, reduce the data forwarding, andimprove the system throughput and the data rate of transmission.

FIG. 6 is a schematic diagram illustrating a method for a MeNB handoverin a small cell system according to an embodiment of the presentapplication, in which a source MeNB determines to handover UE to atarget MeNB and the target MeNB determines the bearer is maintained asbeing established at the source SeNB. It includes the following blocks.

In block 601, a source MeNB sends a handover request message to a targetMeNB. The message carries information of a source SeNB, which mayinclude an identifier of the source SeNB or a cell identifier of asource Scell. The cell identifier may be a cell global uniqueidentifier, or the cell identifier may include a Physical CellIdentifier (PCI) and frequency information.

The handover request message also includes an identifier of the bearer,QoS information of the bearer, UE measurement report and UE capabilityinformation, etc. The source MeNB provides all UE information stored atthe source MeNB, and those information is sent to the target MeNBthrough a handover request message. Then, based on those information,the target MeNB determines whether to select the source SeNB as thetarget SeNB. When the channel quality of the cell of the source SeNB isgood enough and there is an X2 interface available between the targetMeNB and the source SeNB, the target MeNB may determine to select thesource SeNB as the target SeNB, that is, the source SeNB and the targetSeNB are the same, and the bearer established originally at the sourceSeNB is still established at the target SeNB. In the following example,the source SeNB is same as the target SeNB.

In block 602, according to the handover request message, the target MeNBdetermines to continue using the source SeNB as the target SeNB. Thebearer established originally at the source SeNB is not handovered tothe target MeNB, but is maintained at the source SeNB. It can avoidfrequent bearer establishment and release. The target MeNB determines toconfigure the source SeNB as the target SeNB, and the source Scell asthe target Scell. The bearer established at the source SeNB beforehandover is still established at the target SeNB. Or, the target MeNBdetermines to configure the source SeNB as the target SeNB, and thetarget Scell may be same as the source Scell or different from thesource Scell. The bearer established at the source SeNB before handoveris still established at the target SeNB. The target MeNB sends a newkey, i.e., a SeNB KeNB (S-KeNB), to the target SeNB.

The new key is carried in a SeNB addition request message. The SeNBaddition request message also carries information required for RRCconfiguration, such as UE capability, UE configuration information atthe current target Pcell. An address for receiving uplink data may beconfigured as an IP address of the source SGW and a tunnel number.During path switch, MME may send a new address for receiving uplink datato the target MeNB, then after receiving the new address for receivinguplink data, the target MeNB forwards the address to the target SeNB.

In block 603, the target SeNB sends a SeNB addition response message tothe target MeNB. The handover response message carries RRC configurationinformation for UE, and also carries an identifier of the bearer whichis established successfully. If data forwarding is needed for thebearer, the handover response message also carries an IP address and atunnel number for data forwarding. If the bearer is originallyestablished at the source MeNB, the source MeNB sends the data packet onthe bearer to the target SeNB according to the address for dataforwarding. If the bearer is originally established at the source SeNB,the source SeNB sends the data packet on the bearer to the target SeNBaccording to the address for data forwarding. Here, the source SeNB issame as the target SeNB, and the data forwarding is performed within theeNB. The RRC configuration information for UE carried in the messagealso includes configuration information for random access, which is usedfor synchronization between UE and the SeNB. After synchronized, thetarget SeNB starts sending data to the UE.

In block 604, the target MeNB sends a handover response message to thesource MeNB, the message carrying configuration information of thebearer for the UE, which includes configuration information of thebearer at the target SeNB. The message is carried via a RRC container.The handover response message in block 604 also includes the followinginformation:

1. an identifier of the bearer that is established successfully.

2. an IP address and a tunnel number for data forwarding. For the bearerstill established at the source SeNB, the address for data forwarding isconfigured to include the IP address of the source SeNB and the tunnelnumber allocated by the source SeNB, which are obtained at block 603.After the message at block 604 is received, the source MeNB sends abearer release request message at block 606. The message carriers anaddress for data forwarding, in which the IP address is set to be the IPaddress of the source SeNB and the tunnel number is the tunnel numberallocated by the source SeNB. In this way, the source SeNB may be awarethat the data forwarding is an internal data forwarding.

3. The message also carries an indicator of bearer suspending. Thebearer suspending refers to that the bearer is not handovered to the neweNB. According to the indicator of bearer suspending, the source MeNB isaware that a same SeNB is configured by the target MeNB, and the SeNB isnot changed during the handover procedure. The source MeNB sends abearer release request message to the source SeNB, the message carryingan identifier of the bearer and information of bearer suspending.

In block 605, the source MeNB sends a RRC reconfiguration requestmessage to UE.

In block 606, the source MeNB sends a SeNB release request message tothe source SeNB. The message may include an identifier of the bearer tobe released, and may also include an IP address and a tunnel number fordata forwarding. If in the address for data forwarding, the IP addressis set to be the IP address of the source SeNB and the tunnel number isthe tunnel number allocated by the source SeNB, the source SeNB may beaware that the data forwarding is an internal data forwarding.

Or, the source MeNB sends a SeNB modification request message to thesource SeNB, where the target SeNB and the source MeNB are the same, andthe message carries an identifier of the bearer to be released andindication information to indicate whether the bearer is suspended.According to the information, the source SeNB is aware that the beareris established at a same eNB, and the data forwarding is an internaldata forwarding. The address for data forwarding is specified by the IPaddress and the tunnel number for data forwarding. The source SeNBsuspends data transmission at the bearer which needs to be suspended.

In block 607, the UE sends a RRC reconfiguration complete message to thetarget MeNB. The UE also originates the synchronization proceduretowards the source SeNB. This synchronization procedure is not limitedwhen to happen in accordance with the operation in block 607, i.e., thesynchronization procedure can be originated before or after block 607.

In block 608, the target MeNB sends a path switch request message to theMME, the message including the bearer and the corresponding IP addressand TEID for downlink reception, the bearer including the bearersestablished at the target MeNB and the target SeNB. With respect to thebearer established at the target SeNB, the IP address and TEID fordownlink reception for the bearer are allocated by the target SeNB. Themessage is sent from the MME to the SGW, which is same as the existingmethod, and thus omitted herein.

In block 609, the MME sends a path switch response message to the targetMeNB. If the SGW switch is performed, the message includes the uplink IPaddress and TEID allocated by the SGW. The message also includesencrypted information and other necessary information.

In block 610, the target MeNB sends a bearer resuming message to thesource SeNB. After the path switch response message is received, ifneeded, for example, when the address for receiving uplink data ischanged, the target MeNB sends the bearer resuming message to the sourceSeNB. The message may include an identifier of the bearer, and may alsoinclude the uplink IP address and TEID allocated by the SGW. Afterreceiving the message, the source SeNB is aware of the new address forreceiving uplink data, i.e., the uplink IP address and TEID allocated bythe SGW. Then the SGW sends the downlink data to the source SeNB. Afterthe synchronization procedure is completed, the source SeNB sends thedata to UE and receives uplink data from UE.

Using the method as described in FIG. 6, it enables the source SeNB tocontinually work during the MeNB handover process, and to avoid thefrequent bearer release and addition, reduce the data forwarding, andimprove the system throughput and the data rate of transmission.

FIG. 7 is a block diagram illustrating an eNB according to an embodimentof the present application.

Referring to FIG. 7, an eNB may be configured to include a controller710, a radio transceiver 720, a network interface 730, and a memory 740.The radio transceiver 720 may communicate uplink and/or downlink signalswith a UE, and the network interface 730 may exchange information forinter eNB communication with other eNB(s). The controller 710 maygenerate signals and information to be transmitted from the radiotransceiver 720 and the network interface 730, interpret receivedsignals and information, or control operation of the radio transceiver720 and network interface 740, according to at least one of theaforementioned embodiments. The memory 740 may store program codes,instructions, parameters, and the like, necessary for operation of thecontroller 710.

The foregoing only describes preferred examples of the present inventionand is not used to limit the present invention. Any modification,equivalent substitution and improvement without departing from thespirit and principle of the present invention are within the protectionscope of the present invention.

Various embodiments of the present disclosure may be implemented as acomputer-readable codes embodied on a computer-readable recording mediumfrom a particular perspective. The computer-readable recording medium isany data storage device that may store data readable to computersystems. Examples of the computer-readable recording medium may includeread only memories (ROMs), random access memories (RAM), compactdisk-read only memories (CD-ROMs), magnetic tapes, floppy disks, opticaldata storage devices, carrier waves (e.g., data transmission via theInternet), and the like. The computer-readable recording medium may bedistributed by computer systems connected over a network, and thus thecomputer-readable codes may be stored and executed in distributed ways.Furthermore, functional programs, codes, and code segments for achievingvarious embodiments of the present disclosure may be readily interpretedby skilled programmers in the art to which embodiments of the presentdisclosure are applied.

It will be appreciated that the embodiments of the present disclosuremay be implemented in a form of hardware, software, or a combination ofhardware and software. The software may be stored as programinstructions or computer readable codes executable on the processor on anon-transitory computer-readable medium. Examples of the non-transitorycomputer readable recording medium include magnetic storage media (e.g.,a ROM, floppy disks, hard disks, and the like), and optical recordingmedia (e.g., CD-ROMs, Digital Video Disks (DVDs), and the like). Thenon-transitory computer readable recording medium can also bedistributed over network coupled computer systems so that the computerreadable code is stored and executed in a distributed fashion. Thismedia can be read by the computer, stored in the memory, and executed bythe processor. The various embodiments may be implemented by a computeror portable terminal including a controller and a memory, and the memorymay be an example of the non-transitory computer readable recordingmedium suitable for storing a program or programs having instructionsthat implement the embodiments of the present disclosure. The presentdisclosure may be implemented by a program having codes for embodyingthe apparatus and method described in claims, the program being storedin a machine (or computer) readable storage medium. The program may beelectronically carried on any medium, such as communication signalstransferred via wired or wireless connection, and the present disclosuresuitably includes its equivalent.

The electronic device in accordance with the embodiments of the presentdisclosure may receive and store the program from a program providerconnected thereto via cable or wirelessly. The program provider mayinclude a memory for storing programs having instructions to perform theembodiments of the present disclosure, information necessary for theembodiments of the present disclosure, and the like, a communicationunit for wired/wirelessly communicating with mobile devices, and acontroller for transmitting the program to the mobile devices on requestor automatically.

While the present disclosure has been shown and described with referenceto various embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present disclosure asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for managing a connection with a userequipment (UE) by a source master base station in a wirelesscommunication system, the method comprising: transmitting, to a targetmaster base station, a first control message for handover request, thefirst control message including information of a secondary base stationinvolved in a dual connectivity for the UE; receiving, from the targetmaster base station, a second control message in response to the firstcontrol message, the second control message including informationindicating that information of the UE at the secondary base station iskept; and transmitting, to the secondary base station, a third controlmessage for requesting release of resources related to the UE, the thirdcontrol message including the information indicating that theinformation of the UE at the secondary base station is kept, wherein thesecond control message includes the information indicating that theinformation of the UE at the secondary base station is kept, if thetarget master base station determines to keep the UE information in thesecondary base station.
 2. The method according to claim 1, furthercomprising: transmitting, to the UE, a fourth control message for radioresource control (RRC) reconfiguration request to apply a newconfiguration related to the target master base station.
 3. The methodaccording to claim 2, wherein the second control message comprisesinformation for the new configuration related to the target master basestation, and the fourth control message comprises the information forthe new configuration acquired from the second control message.
 4. Amethod for managing a connection with a user equipment (UE) by a targetmaster base station in a wireless communication system, the methodcomprising: receiving, from a source master base station, a firstcontrol message for handover request, the first control messageincluding information of a secondary base station involved in a dualconnectivity for the UE; transmitting, to the source master basestation, a second control message in response to the first controlmessage, the second control message including information indicatingthat information of the UE at the secondary base station is kept; andtransmitting a third control message for addition request to thesecondary base station, the third control message including theinformation of the secondary base station, wherein the second controlmessage includes the information indicating that the information of theUE at the secondary base station is kept, if the target master basestation determines to keep the UE information in the secondary basestation.
 5. The method according to claim 4, further comprising:receiving a fourth message for addition response from the secondary basestation.
 6. The method according to claim 4, wherein the second controlmessage comprises information for a new configuration to be sent to theUE and related to the target master base station.
 7. The methodaccording to claim 4, further comprising: receiving, from the UE, afifth control message for informing radio resource control (RRC)reconfiguration complete; and transmitting, to the secondary basestation, a sixth control message for informing the RRC reconfigurationcomplete.
 8. A source master base station for managing a connection witha user equipment (UE) mobility, the source master base stationcomprising: a radio transceiver configured to communicate the UE; anetwork interface unit configured to: transmit, to a target master basestation, a first control message for handover request, the first controlmessage including information of a secondary base station involved in adual connectivity for the UE, receive, from the target master basestation, a second control message in response to the first controlmessage, the second control message including information indicatingthat information of the UE at the secondary base station is kept, andtransmit, to the secondary base station, a third control message forrequesting release of resources related to the UE, the third controlmessage including the information that the information of the UE at thesecondary base station is kept; and a controller configured to controloperations of the radio transceiver and the network interface unit,wherein the second control message includes the information indicatingthat the information of the UE at the secondary base station is kept, ifthe target master base station determines to keep the UE information inthe secondary base station.
 9. The source master base station accordingto claim 8, wherein the radio transceiver is configured to transmit, tothe UE, a fourth control message for radio resource control (RRC)reconfiguration request to apply a new configuration related to thetarget master base station.
 10. The source master base station accordingto claim 9, wherein the second control message comprises information forthe new configuration related to the target master base station, and thefourth control message comprises the information for the newconfiguration acquired from the second control message.
 11. A targetmaster base station for managing a connection with a user equipment(UE), the target master base station comprising: a radio transceiverconfigured to communicate the UE; a network interface unit configuredto: receive, from a source master base station, a first control messagefor handover request, the first control message including information ofa secondary base station involved in a dual connectivity for the UE,transmit, to the source master base station, a second control message inresponse to the first control message, the second control messageincluding information indicating that information of the UE at thesecondary base station is kept, and transmit a third control message foraddition request to the secondary base station, the third controlmessage including the information of the secondary base station; and acontroller configured to control operations of the radio transceiver andthe network interface unit, wherein the second control message includesthe information indicating that the information of the UE at thesecondary base station is kept, if the target master base stationdetermines to keep the UE information in the secondary base station. 12.The target master base station according to claim 11, wherein the secondcontrol message comprises information for a new configuration to be sentto the UE and related to the target master base station.
 13. The targetmaster base station according to claim 11, wherein the network interfaceunit is further configured to: receive a fourth message for additionresponse from the secondary base station.
 14. The target master basestation according to claim 11, wherein the radio transceiver isconfigured to receive, from the UE, a fifth control message forinforming radio resource control (RRC) reconfiguration complete, andwherein the network interface unit is configured to transmit, to thesecondary base station, a sixth control message for informing the RRCreconfiguration complete.